Prehistoric Earth
Geologic Time
Time __________
Earth’s __________ is divided into time units based on:
• Major __________ events
• Major __________ forms
• Mass __________
-__________- longest time subdivision based on the abundance of certain types of __________
-__________- 2nd longest time __________ based on major worldwide changes in types of fossils. (__________,
Mesozoic, & __________)
-__________3rd longest time subdivision based on types of life that existed __________.
-__________- smallest time subdivision characterized by differences in __________ life.
Organic Evolution
-The fossil record shows that species have changed over geologic __________.
-____________________ changes can affect an organism’s survival.
-Organisms that can not adapt __________ or __________ will not survive.
Species
 Group of organisms that normally __________ with other members of their group.
 Reproduction is the key to the __________ of a __________.
__________Selection
 A process by which organisms with characteristics that are suited to a certain environment have a
better chance of __________ & __________.
 Genetic __________ can help or destroy a species’ survival.
Earth’s History
 Pre__________ Time
 __________ is about 4.5 billion years old.
 __________ portion of Earth’s history (88%) including the Hadean, __________, & Proterozoic Eons.
 Very few __________ are found that date back to 4 billion yrs ago.
 Earth was a ball of __________ for at least a billion yrs.
Primitive Atmosphere
• Atmosphere started out as a lightweight mixture of __________ & __________, which drifted out into space.
• It was replaced by large amounts of __________, Carbon dioxide, Sulfuric acid, & small amounts of Water
Vapor (from __________.)
• Eventually the Earth __________ and the rain formed the __________ oceans.
Precambrian Life
• The first organisms to form on Earth (3.5bya) were __________ that lived in the __________ oceans feeding
on sulfur chemicals.
• Cyanobacteria used __________ for photosynthesis to make food & produce __________.
• Fossils of cyanobacteria are called __________.
• Over millions of years, the levels of Oxygen increased in the __________& __________.
• Current Atmosphere = 79% __________, 20% Oxygen, 1.0% __________, Water Vapor CO2 & other
 Paleozoic Era (__________ mya to 248 mya)
Paleozoic Life
• __________ animals populate the oceans at the beginning of the Paleozoic Era. __________ are the most
abundant.
• Prehistoric __________ fishes become the most abundant organism during the __________ of the Paleozoic.
• __________ take control at the end of the Paleozoic.
• __________ & cone-bearing plants (Gymnosperms) grow on land.
• Early forms of __________first appear on land near the end of the Paleozoic.
Paleozoic Geology
• __________ forms near the end of the Paleozoic.
• The largest ____________________ in Earth’s history kills 90% of all marine life & __________of land species
(Permian Period.)
 Mesozoic Era (248 mya to __________ mya)
Mesozoic Life
• Reptiles (Dinosaurs) most __________ organism on Earth.
• Reptiles are the 1st __________ to live entirely out of the water.
• The 1st __________ appear during the Triassic Period
• The 1st __________ evolve from dinosaurs during the Jurassic Period.
• The 1st flowering plants (__________) evolve during the __________ period.
Mesozoic Geology
• Pangaea breaks apart into ____________________ & Laurasia during the early Mesozoic.
• The 2nd largest ____________________in Earth’s history kills many marine & land species including the
dinosaurs.
• Many factors could have led to the __________:
• Plate Tectonics causing __________changes
• __________Asteroid hit the Earth
• Blocking out of the __________
• __________temperatures
• __________
Cenozoic Era (65 mya to ____________________)
Cenozoic Life
• __________ become the most dominant organism on Earth.
• 3 groups of mammals evolve:
 __________
 Marsupials
 __________
 The largest of the mammals becomes __________ during the Cenozoic.
 Homo sapiens appear about 140,000 years ago (according to the fossil record) and becomes the
most dominant/__________ animal.
Fossils
Principle of Superposition
 In __________ rock layers, the oldest layers of rock are on the bottom.
 Rock layers can be ranked by __________ age.
Forming Fossils
 An organism must be __________ quickly to form a fossil.
 Hard parts dissolve to leave __________.
 A __________is formed when a mold fills w/ sediment or minerals.
 Thin __________ films remain in the shapes of dead organisms.
Fossil Type
Description
__________
hollow impression of a living thing in rock after it rots away
__________
solid mineral deposit that filled a mold, leaving a copy of the living thing
__________
an impression in rock made by a living thing during its life activities
__________
plant or animal tissue replaced by minerals
Whole __________
an entire plant or animal encased and preserved in ice, sap, or another material
__________
remains of tracks, burrows, eggs + eggshells, nests, droppings, etc
Dating Fossils
__________ Decay
• Some __________ are unstable and decay into other isotopes & particles.
• Decay is measured in ____________________, the time it takes for half of a given isotope to decay.
Radiometric Ages
• The ratio of the parent isotope to daughter product can be used to determine the __________ age of the rock.
• Living organisms less than __________ years old can be dated using Carbon-14.